An optical scanner includes a light source, an optical part, a housing, and a retainer. The light source projects light against a target. The optical part is disposed on a light path between the light source and the target. The housing houses the light source and the optical part. The retainer fixed to the housing holds the optical part and includes a plurality of flanges disposed along an outer circumference of the retainer. One of the plurality of flanges of the retainer is adhered to the housing an adhesive agent. An image forming apparatus includes the optical scanner.